<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 内联样式/行内样式 -->
    <div style="width: 100px;height: 100px;">块级元素</div>
    <!-- 内部样式表 -->
     <style>
        /* @import url(./outer.css); */
        div{
            background-color: red;
        }
     </style>
     <!-- 外部样式表 -->
      <link rel="stylesheet" href="./outer.css">
</body>
</html>